1. Field of the Invention
The present invention relates to orthopaedic implants and, more particularly, to a method of making orthopaedic implants having a porous surface connected thereto by a process utilizing an organic binder compound.
2. Description of the Related Art.
Orthopaedic implants of known design may be constructed, e.g., of cobalt-chromium-molybdenum or titanium. Such materials provide suitable physical characteristics of strength, corrosion resistance, wear properties and biocompatability for use in orthopaedic applications.
It is also known to provide an orthopaedic implant with a porous surface at the exterior thereof The porous surface may be used to promote bone ingrowth and thereby enhance implant fixation within the bone. Alternatively, the porous surface may receive bone cement therein to enhance implant fixation within the bone. Such porous surfaces may be constructed, e.g., of metal beads or fiber metal mesh which are sintered, diffusion bonded or welded to the implant to form an integral part of the implant.
Presently, fiber metal mesh used to form a porous surface is pressed into a desired shape and maintained under pressure during the sintering process in which some of the fibers are bonded together to form a pad. The process may also be referred to as diffusion bonding. The metal pad is shaped to correspond to its supporting surface and is then positioned in contact with an implant and clamped in place during a sintering process. Alternatively, the fiber metal pad may be gravity sintered, thereby eliminating the use of external clamping forces. A similar process may be employed when making a porous surface using metal beads.
Sintering the porous surface layer to the implant with external pressure is time consuming and expensive for the manufacturer. During sintering, the ramp up and cool down time for the furnace is approximately 14 hours per cycle. If the porous surface layer is being connected, for example, to the interior bone engaging surface of a femoral knee component, it may take 4 complete cycles. The complex geometric interior design of the femoral knee component requires that only one or two pads be attached during one cycle. The typical interior of the femoral knee defines 5 distinct surfaces which require a porous coating. Therefore, to completely bond all of the porous surface layers to the interior of the femoral knee component would require in excess of 56 hours of furnace time. Added to that time is the time required to connect the clamp tooling to the implant for holding the pad in contact with the implant. From the above description, it is clear that providing a porous surface layer on an implant using existing technologies is time consuming and expensive for the manufacturer of orthopaedic implants.